I had an issue with an MSCS SQL cluster a while back where the "Volume Manager Disk Group" resource disappeared from the selection drop down! This was not cool as I needed the resource as a dependency of my SQL cluster I was about to setup.
The solution was fairly easy, but most certainly NOT obvious. Here's what you need to do:
Drop to a command prompt and type... (hit enter after each line)
cluster restype "Volume Manager Disk Group" /Delete /TYPE
cluster restype "Volume Manager Disk Group" /CREATE /DLL:vxres.dll /TYPE:"Volume Manager Disk Group"
After that's done you should see the resource available in the drop down box. If it matters, this was done on Windows 2003 SP2 R2 x64 Enterprise Edition.